(a) Field of the Invention
The present invention relates to a semiconductor apparatus and more specifically to an overheat protection device and a semiconductor switching apparatus using the overheat protection apparatus, and an intelligent power module.
In more concrete terms, this invention relates to a semiconductor switching apparatus, which has a drive circuit to drive a load according to a load drive instruction entered from an input terminal and to control or cut off a load drive power according to a gate control signal; and an overheat detection circuit that generates an overheat detection signal when it detects an overheat state of the drive circuit.
This invention also relates to an intelligent power module, which includes a power MOSFET as a drive circuit to drive a load according to a load drive instruction entered from an input terminal and to limit a load drive power according to a gate control signal; a temperature detection diode provided near the power MOSFET to detect the overheat state of the power MOSFET; and an overheat detection circuit having a comparator for generating an overheat detection signal upon detecting an overheat state.
(b) Description of the Prior Art
FIG. 5 is a circuit showing a conventional intelligent power module having an overheat protection function.
The conventional intelligent power switch circuit of this kind, as shown in FIG. 5, includes: a power MOSFET 5 which supplies electricity from a drain (in the figure, a terminal D; a source S is connected to a ground) connected to a battery (not shown) to a radio and car computers on board an automobile according to the load drive instruction entered from the input terminal (in the figure, a terminal G); a temperature detection circuit 1 that generates an overheat detection signal upon detecting the overheat state of the power MOSFET 5; a self-hold circuit 2 that generates a gate control signal to perform a protection control by deenergizing the power MOSFET 5 according to the overheat detection signal; and a gate cutoff circuit 3 that deenergizes the power MOSFET 5 by cutting off the load drive instruction supplied to the gate of the power MOSFET 5 according to a gate control signal.
FIG. 6 is a timing chart showing the operation of the overheat protection device in the intelligent power module of FIG. 5.
In the intelligent power switch circuit with the above configuration, when the temperature detection circuit 1 detects the overheat state of the power MOSFET 5 (i.e., the overheat detection signal in FIG. 6 changes from an OFF state to an ON state) while the power MOSFET 5 is supplying electricity to the load according to the load drive instruction (see Vout.sub.-- 1 or Vout.sub.-- 2 in FIG. 6), the self-hold circuit 2 generates a gate control signal according to the overheat detection signal to cause the gate cutoff circuit 3 to cut off, through an internal resistor 4 according to the gate control signal, the load drive instruction that is supplied to the gate of the power MOSFET 5, thus deenergizing the power MOSFET 5.
In more detail, as shown at Vout.sub.-- 1 of FIG. 6, the conventional intelligent power switch circuit performs the power control (i.e., switching control) to cut off the electricity supplied from the power MOSFET 5 (in the figure, Vout.sub.-- 1) according to the overheat detection signal (i.e., transition from OFF state to ON state).
In such a switching control, the cancel of the cut-off control state of the power Vout.sub.-- 1 is performed by the self-hold circuit 2 being reset when the load drive instruction (IN signal) changes from the OFF state to the ON stage again.
The conventional intelligent power switch circuit, as shown at Vout.sub.-- 2 of FIG. 6, performs a power control (i.e., power limit control) to limit electricity (in the figure, Vout.sub.-- 2) supplied from the power MOSFET 5 by turning it on and off according to the overheat detection signal that is generated (i.e., it changes from the OFF state to the ON state) when the temperature exceeds a predetermined temperature as a threshold.
Such a power limit control resets the limit control state of the power Vout.sub.-- 2 when the self-hold circuit 2 is reset by the transition of the overheat detection signal from the ON state to the OFF state.
However, such a conventional intelligent power module has the following technical problem. In the switching control, only after the load drive instruction (IN signal) changes its state from OFF state to ON state, is the self-hold circuit 2 reset to cancel the cutoff control state of the power Vout.sub.-- 1. Hence, if the overheat state is eliminated while the load drive instruction (IN signal) is ON, it is difficult to immediately execute the resetting of the cutoff control state.
When the ON state of the load drive instruction (IN signal) is maintained for a long period, in particular, even if the overheat state is eliminated during the ON state, the cutoff control state is maintained, making it difficult to execute the immediate resetting of the cutoff control state.
The power limit control of the conventional intelligent power module is performed by turning on and off the power Vout.sub.-- 2 supplied from the power MOSFET 5, with a predetermined overheat temperature used as a threshold, to limit the power Vout.sub.-- 2 until the self-hold circuit 2 is reset by the elimination of the overheat detection signal (i.e., transition from the ON state to the OFF state). Therefore, a problem arises in which the ON/OFF switching of the power Vout.sub.-- 2 during the time from the occurrence of the overheat detection signal to its resetting (i.e., the time during which the overheat detection signal changes from the OFF state to the ON state to the OFF state) causes thermal stresses in the power MOSFET 5.
This makes it difficult to perform immediate resetting of the power limit control state upon elimination of the overheat detection signal (i.e., transition from the ON state to the OFF state).